The following formula subtracts the date of last previous draw of 0% from the date of the current draw of 0%:
Formula: copy to clipboard 
=IF(AND(C2<0,C3=0),A3-INDEX(A$2:A2,AGGREGATE(14,6,(ROW(A$2:A2)-ROW(A$1))/((C$2:C2=0)*(C$3:C3<0)),1)),"-")

Note that in the sample file every day between 4-Jan and 4-April is listed so the results will be the same as those yielded by Bernie's formula.
Let us know if you have any questions.